Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
{\left( {2x - 3} \right)^3} - {\left( {5y + 2} \right)^3}\\
= \left[ {\left( {2x - 3} \right) - \left( {5y + 2} \right)} \right].\left[ {{{\left( {2x - 3} \right)}^2} + \left( {2x - 3} \right)\left( {5y + 2} \right) + {{\left( {5y + 2} \right)}^2}} \right]\\
= \left( {2x - 5y - 5} \right).\left[ {\left( {4{x^2} - 12x + 9} \right) + \left( {10xy + 4x - 15y - 6} \right) + \left( {25{y^2} + 20y + 4} \right)} \right]\\
= \left( {2x - 5y - 5} \right).\left( {4{x^2} + 10xy + 25{y^2} - 8x + 5y + 7} \right)\\
b,\\
2x\left( {5x - y} \right) - 15x + 3y\\
= 2x\left( {5x - y} \right) - \left( {15x - 3y} \right)\\
= 2x\left( {5x - y} \right) - 3.\left( {5x - y} \right)\\
= \left( {5x - y} \right)\left( {2x - 3} \right)\\
c,\\
4\left( {x + 2} \right) - 2x - 4 = 0\\
\Leftrightarrow 4.\left( {x + 2} \right) - 2.\left( {x + 2} \right) = 0\\
\Leftrightarrow 2\left( {x + 2} \right) = 0\\
\Leftrightarrow x + 2 = 0\\
\Leftrightarrow x = - 2
\end{array}\)
